Method of making bourdon tube instruments



July 26, 1949'. U F. L. FAHY 2,477,242

METHOD OF MAKING BOURDON TUBE INSTRUMENTS I Filed July s, 1946 v 2 Sheets-Sheet 1 July 26, 1949. F. L. FAHY METHOD OF MAKING BOURDON TUBE INSTRUMENTS Filed July 8, 1946 2 Sheets-Sheet 2 Manchu a slew] ff'xi'iovement t moms m 8. ,mtary' stain, wlm'wh Patented July 26, i94

emits-a STATES PATENT OFFICE.

OF MAKING BOURBON TUBE msmnmm'rs 7 Lt Fab-y; Bmidgepott. Coma, assifinoi: to r Manning, Maxwell & Moore, Incorporated, New York, N, Y. a eo zzgqrattfon 0i New ersey anaemia hiys, 1946; Serial we 682,113

aim: we to a mama at malts k msminstrmnenteitms the human mm (which is aiemth oi mm-e mm Fsiltent whim; at one end ei'ireeht amatmte:

sum-ant movementet its fine em! or tip (the an. is transmitted by the ta an: index with; a udiak it indieate the variations 21.2mm: the m Emmi-ever;

it is vew dimwtte'rmazmfimure Eamon; time: which are macaw, with respect: te dimemwm mi: toi. intenneai pleasure variations). Mexeoventhe. tta at the tube iii-p mavement 111w pf -the index slang, the; dial; so asto insure equak traveioi the index (oven the intimscale) in respense zmk my wasid if-mama isattendedzmth able wheziidials were cost of manuiactuse v v 7 She pisimipar obieet o: the present mention isto wavidea-mvekmethoot aBourdan tubeinstmment thenehy thezamountoireuuined aiter assembly of; the instnumegit is minced; to a mmimum. A further abject isto I was a methed of Beumleim tubes w nebw the efiects of. slightvmatiensi the *1 .dimensions at tlwtubes are substantialiy -A- urthes objectis to wavide a method 02 mm tube such that the accurate location of. the: fnee end. or tip at the unstressed tube and the woven direction oi; tnavel of the tip in response to pressure variatiens 1's The principle); invention. and eeztain de isiizati'a of this pnincipie ane iilusqfixated in the accemganying draw!!! Fig, 1" is & diagnammati'c imnt elevation shewinett iw: tube instiument such for example as a pres-sure gauge- 01: thermometer; V

Fig.1 2 a diiagrammatiefrqnt elevation illustratin-g the step at cutting Bourden tubes to uni- Ieirm: pacedeterminedi arcwate Lengths in aecam amzewith: thepraetiee of the present invention;

7 Fig. 3 isa. diagrammatie front elevation. SHOW" ing how: the tube, after: being cutie proper length, is fixedteabmeketmemher; 7.

- Fig. 4: is a diagrammatic front el evatiett showim'g! the time: with bracket memben assembled with. @the: parts of thseinstnuament;

E15. 5 is a: diagxiami illmfltratimxgla..slighrtly ditfierent prmeihnre in; accezd'anee" the; present invention- 4 v Fig: 6: isa: diagizamatic 11mm elevation show ing the practical application of" the pmcedui e iiatustratect inFig. 5;

e i is a front eieiiatiom. partly in. menskewing the step of limiting; the time ten the tih' bracket and ta its suhpfirt; and

Fig. 8 aidiagram illustrating cei tain relations between: the fastens ihvewem Owing-t0 the: Spring-back? of the resilient metal emr'pleyem it is by pmduetim methods; as above: mated, ta make Eoui don tiil's'es which: are alike as w radius e-f cunva tuice; it likewise mun: to make tuflo'eswhich nespmidi in exaetty the same-way -to the same pressuregdi fierential it other wards, to make times wimse tips travel in the same: direetian and te the extent in respbnse to a given zange at change;

However;- it is amaecepted fact; that the angle between the tangent to the free; end; portion 01' tip of the tube 'and the line or direction tiff travel of the tube tip is a function 'oi the arcuate of the; e'fieetiwepertitm efi the tube. This relation ismade use of in accm'd'ance' with the: present iiwention such a way as to=eii minatsmist on? the diiiieiaiti'es heretofore experienced the pieduetien of accurate instruments In utilizing this principle; advantage is talren f the fact that by geqmetrie methods; assisted in certain particulars by trial" and error it is possihie "to, design an arrangement of the coitstituent parts of the movement mechanism (incl'udi'ng' the l'ngth of' the motion-transmitting link) which, 01: ahB'ourdbn tube havihg known nesul'ts in optimum aceunraey. Thus by location at the tube tip, and by insuring the mevemen-t 0f the tube tipin apt-edetermined. it becomes, pnactieakly possible to malf e instnuments upezn. a produeti'on 3 basis which are acceptably accurate with a. minimum of necessary calibration.

Specifically and as one solution of the problem, the tube, after bending, is cut to a predetermined arcuate length. The tip of the tube is then located accurately (at a predetermined point) with reference to the axis of the index staff and the opposite end of the tube is so fixed that the tangent to its free end is oriented to a predetermined angle.

In Fig. 1 the essential parts of a Bourdon tube instrument and their geometrical relation are diagrammatically indicated. In this view there is indicated a dial, graduated for example to a uniform scale, and which cooperates with a pointer or index 2 mounted on a rotary stall 3 and which customarily swings through an arc of 270 over the scale. The staff is provided with a pinion 4, which meshes with a segment gear 5 carried by a lever B mounted on a rotary staff I and having a tail piece 8 which is connected by a link 9 to the tip bracket I of the Bourdon tube B whose free, closed end II carries the tip bracket and whose opposite end I2 is fixed to a support I3 and whose interior communicates with a capillary tube or other conduit for transmitting pressure to the interior of the tube. The arcuate length of the curved portion of the tube B, when in the unstressed condition, as herein illustrated by way of example, is approximately 270, (although it may be of other arcuate length) the tangent to the free end. or tip II of the unstressed tube being indicated by the line I4 and the path of travel of the tip, as the internal pressure increases, being indicated by the line I5, the angle between these two lines being designated by the letter A.

The geometric layout, whichpermits accurate and easy calibration of the instrument with respect to a predetermined dial layout, for instance a uniformly graduated dial, is quite readily determined, assuming that the direction of tip travel is definite and that the minor departures from theoretically correct tube curvature, due

to manufacturing inaccuracies, may be neutral ized. This geometric relation involves the distance between the axes of the staffs 3 and l, the effective length of the tail piece 8, the length of the link 9, and the exact location of the tip of the unstressed tube, as referred, for example, to its distance from the axes of the staifs 3 and I, and the direction of the path of travel I5 of the tube tip as referred, for example, to a line Joining the axes of the staffs 3 and I. The effective length of the tail piece 8 is varied in accordance with variations in the length of tip travel.

Herein when reference is made to the tube tip it is to be understood that the axis of the pivot which unites the link 9 to the free end of the tube is to be considered as the tube tip, a1 though this pivotal axis in practice is usually located in the bracket II! which is not a part of the tube proper, but which is fixed to the latter.

The method of locating the several parts above described is familiar to those skilled in the art, and forms no essential part of the present invention. However, in order to build instruments by production methods, which do not require excessive calibration when using predetermined dial layouts, the method of manufacture must be such as in each instance to insure the proper initial tip position and the proper direction of tip travel upon which the geometrical layout is based. As above pointed out, the present invention achieves this result by reference to the fact that there is a definite relation between the arcuate length of the Bourdon tube and the angle A between the tangent I4 to the tube tip, and the direction I5 of tip travel. Thus if the tube be cut to a determined arcuate length, and if the tip endofthe tube be mounted s that-its tangent I4- at a definite angle referred to the geometrical layout, the direction l5 of tip travel will also make a definite angle K (Fig. 8) with respect to factors of this geometrical layout, for instance with reference to a line joining the axes of the staffs 3 and I, it being understood that in mounting the Bourdon tube its free end or tip will be accurately located with respect, for example,to the axis of the staff I.

Referring to Figs. 2, 3 and 4, the characters B and 1? indicate Bourdon tubes of slightly different radii of curvature representing in this respect (but greatly magnified) diiferences in radius, for example, within a range of the order of one-eighth inch, which may be expected in tubes made by present commercial methods but intended to have the same radius and intended for use in'a given instrument. It will be obvious that the intended radius of the tube is determined by the available space within the. case of the instrument which is to be made, and will thus depend upon the size of the case as a whole, the design of the movement mechanism, and the possible presence of other devices within the same case. In accordance "with one mode of procedure in the attainment of the objects of the present invention, the free end portion- II of the selected tube is clamped between fixture jaws I6 and N (Fig. 3) which substantially conform to the curvature of the ideal tube and thus determine the location of its center of curvature. The opposite end I2 of the tube, that is to say, that end which is to be'fixed'to the mounting bracket, is now out off along-a line I8I 8 parallel to the direction I5 of tip travel and pass ing through the center of curvature of the tube. A mounting bracket I9 is provided having -a fiat surface 20 for contact with the cut end of the tube, and: this surface 20 of the bracket is now caused to register with the line I8I8 and the cut end of the tube is soldered or'otherwise permanently secured to the bracket I9. This bracket is provided with an opening'wlu'ch communicates with the -interior'of lthetube'when the end I2 of the tube'has beenfixed in place,-and a capillary tube 2| or other'lconduit is sealed in the opening and-is arranged to supply pressure fluid to the interior of the Bourdon tube. In the final assembly of the tube (Fig. 4) with the'gauge parts, the bracket I9 fis mounted up'on'the support S for the gauge movement, with the surface 20 disposed accurately 'parallel to-the intended direction I5 of up travel, and the -bracketl9 is then permanently fixed to the "support S by welding, soldering or thelike. In this 'de'scrip tion' it is to'be understood that the support S is representative of anyframe member which carries the movement mechanism, and that the bracket I 9 is representative of any customary support for the fixed end of the tube.

Referring to Figs. 5, 6' and '7, 'a second mode of procedure in accordance with the presentinvention is illustrated. Thus referring to Fig. 5, the characters B 3* and B indicate Bourdonftubes of different radii of curvature, thus representing the differences (much magnified), in "tube, diameter which are'met within the commercial 76 practice of gauge-making. "Those ends'of these tubes which-are to be securedto the; fixed supp rh-ar'e indicatedas locatedat'the common point 21 while thefree ends of the tubes "are spaced apart due to the differences in tube diameter. When thus-arrangedja line, suchas the line 28-29, passing through the point 21 and-through the tube tips 30, 3! and 32, cutsofl'lngths of the several tubes which are of the same arcuate length, that is to say, ofthe same number of tie grees of" arc. With the understanding that each of the tubes; is of the same degree of': arc, the direction of travelof the several tube tips be represented by the" parallel lines 33 34 and" 35, respectively. In the particular i-nstance illustrated these lines are perpendicular to-those radii of-the respective tubes which extend from the centers 22', 23' and 24"of the respective tubes, to the tube tips 30, 3t and 32 respectively. Upon the basis of the above relationships, the procedure, in accordance with the present invention, is'illustr'ated from thepi'actical standpoint in Figs. 6 and'l. Thus-for example, referring to Fig. 6, and assuming that either one or the other of tubes 13 or B is the one selected, the end 36 of the selected tube (which is to be the fixed end) is arranged in a fixture comprising stop members 31' and 31 the latter having a vertical surface 38 and the end 36 of the tube being butted against this surface 38. In the arrangement illustrated; the direction of tube travel (indicated by the line 33) for the selected tube TB is parallel-to' the' surface 38. "The righthand end'of the selectedtube B is then: trimmed ofl? along the line- 28'-29 (the angle which this line makes with'the surface 38. being the same in trimming all tubes, thus assuring the produc tion of tubes, regardless of radius variation, which are all of the same arcuate length). An internal support for the tube may be provided. Preferabl this support has tube-engaging-rolls 39 and 40 carried by a vertically slidable'member which is urged upwardly by a spring. However, the strength or this spring is insufi'icient to produce any appreciable deformation of the tube. -:.'Dur ing the cutting, the tube, whoseend '36 is: still accurately positioned by the/fixture, is; held immovable by any suitable means, for instance by clamping plates applied to opposite faces of the tube. A tube tip bracket G (Fig. 7) is provided, having an elongate fiat surface 42 and having the opening X for the reception of the pivot pin by means of which the bracket is secured to the transmitting link 9 (Fig. 1). This bracket G is now moved (with its surface 42 in the line 28-29) until the axis of the pivot opening X occupies the proper relation to the other parts of the movement mechanism in accordance with the geometric layout of Fig. l. The tube tip is now permanently secured to the bracket G by solder or similar means, the bracket G being held firmly in position by an appropriate fixture While this operation is being carried out.

Obviously, instead of moving the bracket G relatively to the tube tip, the tube tip might first be fixed to the bracket and the opposite end 36 of the tube properly adjusted relatively to its supporting bracket, for example, the nipple N, before attaching it to the latter, it being understood that in the latter event the support N will have an extended surface in the line 38 (parallel to the line 33) for contact with the end of the tube.

It is thus evident that the invention may be carried out in various specific ways, the principal and most essential feature being that in accordance wlth: this procedure the? direction of tip travel remains-parallel ELY-8} direction which has been predetermined in: the geometrical layout, or inother words, the radius: from the conter of any given tube: to its tip-must be parallel to a predetermined: directionint-the geometrical layout, and assembly. I I 1 Obviously, the tubes employed in making a given-size and style" of instrumentzwillzbeselected fromtubes such as are prepared by' customary commercial practice for use in instruments of the desired size and style, and will differ from each other only-within a rangeof difference herc in referred to asthe pe rmis'sive range, such as re sults from imperfection iii-manufacture, bycommercial-methods; of tubes designedto besum stantially alike in dimensions" in response to internal pressure-variations.

I claim: i

'1. That method of'lhakin'g Bourdon tube instruments having uniformly graduateddialsand employing Bourdon tubes madcbyproduction methods such that tubes of the same intended radius of curvature differ from one another in actual radius, said method" comprising as; steps determining, by known. procedures, thecorrect geometrical layout. for: the. particular size and style of instrument; to: be made, including. the properlocation :of theltubeitipg theproper directionof. travel of the tube tip-and the theoretically correctv radius. of Bourdon tube for in: the particular instrument to lee-made, cutting all of the tubesaccuratelyto the same arcuate length by: providing: a fixture having means for: locatin one end of thetube soithat'the: center of. cur-Va ture of a tube mountedthereinis; properly p0si-. tioned in accordance; withv the; geometric; layout, mounting one end of the tube in said fixture, rigidly holding the, tube whilecutting: the opposite end of the tube in aplane bearing a definite relation to the direction of the tip travel as determined bythegeometric lay-out, the plane of out being the-same for all tubes, and perman'ently securing a bracketto. thecutend of the tube.

. 2. That method of making tube. instruments having pregraduated dials and employ ing Bourdon tubes made by production methods such that tubes of ostensibly the same radius of curvature differ from one another in actual radius within a range of the order of one-eighth inch, said method comprising as steps determining, by known procedures, the correct geometrical layout for the particular size and style of instrument to be made, including the proper location of the tube tip, the proper direction of travel of the tube tip and the theoretically correct radius of Bourdon tube for use in the particular instrument to be made, providing means for positioning one end of the tube which has been selected for use so that the center of curvature is properly located with reference to the geometric layout, mounting one end of the tube in said positioning means, holding the tube stationary while so positioned and, while so holding it, cutting off material from its other end in a plane which bears a definite relation to the direction of tip travel as defined by the geometric layout thereby to provide a tube of accurately predetermined arcuate extent, and permanently attaching a bracket member to the cut end of the tube.

3. That method of making Bourdon tube instruments having uniformly graduated dials and employing Bourdon tubes made by production methods such that tubes of the same intended radius of curvature differ from one another in actual radius within a range of the order of one-eighth inch, said method comprising as steps determining, by known procedures, the correct geometrical layout for the particular size and style of instrument to be made, including the proper location of the tube tip, the proper direction of travel of the tube tip and the theoretically correct radius of Bourdon tube for use in the particular instrument to be made, providing tubes by production methods of ostensibly the correct radius of curvature but which in fact difier slightly in radius, accurately cutting each tube to the same arcuate length and, in assembling a given tube with the other parts of the instrument, disposing the free tip of the tube at the exact location determined by the geometrical layout, and permanently fixing the opposite end of the tube to a rigid supporting member.

4. That method of making Bourdon tube instruments having uniformly graduated dials and employing Bourdon tubes made by production methods such that tubes of the same intended radius of curvature differ from one another in actual radius, said method comprising as steps determining, by known procedures, the correct geo-' metrical layout for the particular size and style of instrument to be made, including the proper location of the tube tip, the proper direction of travel of the tube tip and the theoretically correct radius of Bourdon tube for use in the particular instrument to be made, cutting all of the tubes accurately to the same arcuate length by so positioning and rigidly holding that end of the tube which is to be the free end that the center of curvature of the tube is properly positioned as determined by the geometrical layout, cutting the opposite end of the tube along a line parallel to the direction of tip travel as determined by the geometrical layout, providing a mounting bracket having a substantiallyflat face, disposing said face in a plane parallel to the direction of the path of tip travel and at the same distance from the latter as the plane of cutting, contacting the cut end of the tube with said bracket surface and permanently fixing it thereto, disposing the tube tip at the proper location as determined by the geometrical layout, and permanently fixing the mounting bracket relatively to the support for the movement mechanism.

5. That method of making Bourdon tube instruments having uniformly graduated dials and employing Bourdon tubes made by production methods such that tubes of the same intended radium of curvature differ from one another in actual radius, said method comprising as steps determining, by known procedureathe correct geometrical layout for the particular size and style of instrument to be made, including the proper location of the tube tip, the proper direction of travel of the tube tip and the theoretically cor- ;rect radius of Bourdon tube for-use in the particular instrument to be made, and cutting all of the tubes accurately to the same arcuate length by providing a fixture for positioning that end of the tube, which is to be the fixed end in the completed instrument, so that the center of curvature of the tube is properly located in accordance with the geometrical layout, placing one end of the tube in the fixture and rigidly holding it while cutting ofi material from its opposite end, the plane of cutting being the same in cutting each tube and passing through the position of the tube tip as determined by the geometric layout, providing a tip bracket having an extended fiat surface and means defining the pivotal axis for a motion-transmitting link, disposing the bracket so that said axis is at the proper location as determined by the geometric layout, contacting said flat surface of the tip bracket with the cut end of the tube, and permanently securing the tube to the bracket.

FRANCIS L. FAHY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,797,324 Carliss Mar. 24, 1931 1,894,153 Brietzke Jan. 10, 1933 

